1. Field of the Invention
The present invention relates to a bonding machine and more particularly to a bonding machine which includes a pipe system for preventing oxidation of workpieces placed on a bonding stage.
2. Prior Art
In prior art outer lead bonding, for example, as shown in FIG. 4, when leads 2, which are connected beforehand to electrodes of semiconductor device 1, are bonded to substrate 3, the substrate is first set on a bonding stage 5, and then a semiconductor device 1 that has the leads 2 is placed on the substrate. Bonding tool 8 is lowered and presses down the leads 2 onto the substrate 3, thus performing the bonding. The bonding stage 5 includes heat block 6, which contains a heater, and a hot plate 7.
However, if the workpiece 4, which comprises the semiconductor device 1, the leads 2 and the substrate 3, is entirely or partially made of a material such as copper, it can easily be oxidized when it is heated by the bonding stage 5. In order to prevent oxidation, a reducing gas or an inert gas (hereinafter collectively called "gas") is blown out of nozzle 9 to the workpiece 4.
The Japanese Patent Application Laid-Open (Kokai) No. 53-10268 is a prior art which discloses a bonding machine wherein gas is blown out of a nozzle to a workpiece.
The prior art device shown in the accompanying FIG. 4, however, has problems. Since the gas is blown onto the workpiece 4 from only one side that faces the nozzle 9, the gas cannot reach the other side. In other words, a uniform gas atmosphere which covers the entire surface of the workpiece cannot be created around the workpiece, resulting in poor oxidation prevention.
The device disclosed in the Japanese Patent Application Laid-Open (Kokai) No. 57-190328, for example, solves the problem. In this prior art, a blow pipe having gas discharge holes that are opened to face workpiece is provided around the bonding stage so that the pipe surrounds the entire workpiece and discharges the gas onto the workpiece. Thus, since the blow pipe surrounds the entire workpiece, a uniform gas atmosphere can be created around the workpiece.
However, even the piping system of this prior art has problems. Since the gas route is formed continuous, the gas supplied into the blow pipe tends to flow backward. If the back-flow occurs, a pressure difference results at the supply end and terminal ends of the blow pipe, which causes a non-uniform gas atmosphere around the workpiece.